Thanks your remind and I agree it's strange also.
Can you show the result of
show ip ospf database externa 158.1.0.0
on SW4? I wanna to know which router redistribute this route to SW4
Regards,
Howard

I already replied to this - but just in case the reply didn't make
it, here it is again:

Of course - the subnet is redistributed by R3 (the router at the
other end of the two areas), using a "redistribute connected" statement
(in the original lab, the subnet was redistributed from EIGRP, with the
same result).